Prime Minister John Key says his hard working ministers deserve their taxpayer-funded Wellington homes but he isn't happy with the rules that cover their claims.

His response to criticism of their hefty allowances has been to order a review of the "arcane" regulations and he says he wants changes that will be fair to taxpayers and ministers.

Ministers who have attracted the most attention are those who own homes in Wellington but rent them out while they live in taxpayer-funded houses.

MPs clocked up expenses totalling $7.5 million in the first six months of this year and they're insisting it was money well spent.

Even ACT MP Sir Roger Douglas, who took his wife on an overseas holiday, had no regrets about putting 90 percent of the airfares on taxpayers.

He told reporters he gained that entitlement as a former MP in the 1980s.

"I was spending time with my son and grandchildren," he explained before he started to lose patience with questions about whether it was a good idea during a recession.